Tallow is rendered beef or mutton fat (suet).
Unlike suet, tallow can be stored for extended periods without refrigeration, provided it is kept in an airtight container to prevent oxidation.
It is used to make soap, for cooking, as a bird food, and was once used for making candles.
In the fats and oils industry fats may be classified as tallows or greases, depending on their melting point (their titre).